The present invention generally relates to the field of communications networks, and more particularly to a method for facilitating communications between resources on a multichannel network by determining appropriate time slots and channels on which to transmit a message so that it will arrive at its destinations at a time when it may be received.
Time Domain Multiple Access (TDMA) communications systems allow multiple users to communicate through a Demand Assigned Multiple Access (DAMA) multiplexer over a network using a common communications path. A DAMA multiplexer is TDMA connection between a user baseband device (Teletype, Phone, FAX, etc.) and a communication system such as a local area network (LAN) or satellite relay system. A DAMA multiplexer retains send and receive data in a holding buffer until the specified time slot for communications occurs. The data then is burst in or out of the buffer at a much higher rate to facilitate a perceived constant communications path. Messages are sent during specific time slots which comprise a periodic time frame, or TDMA field.
The TDMA field of each time frame includes a timing mark to identify the beginning of each time frame and is followed by multiple time slots. In the past, DAMA multiplexers allowed both distributed (DC) and automatic (AC) control modes.
In the DC mode, users simply connect themselves to the communications fields (time slots) they are interested in. However, there are problems associated with this relatively unstructured method of communications. For example, unauthorized users could connect to private communications, constant key offenders jammed the time slots, and no policing of control and order existed. A request for a new circuit could take weeks to be assigned. Most users would leave circuits connected to a time slot even though they were not being used. These shortcomings resulted in the inefficient use of communications channels, particularly of the type used in UHF satellite communications systems.
AC mode provides a single point of control like a telephone system. In the AC mode, all communications must request connection to a specific group or user terminal(s) identified by address(es). This allows more flexibility for creative connections including communications amongst various different channels, and device matching (phone connected to another phone) for preventing jamming or interference from unknown sources. In that system, connections are made in less than five seconds if time slots are available. However, when operated in the original AC mode, the DAMA controller was a person-intensive system requiring the controller to be manned 24 hours a day, and was prone to failure. The AC mode DAMA channel controller was a manual system requiring a human to make intelligent decisions as to where to place requesting users on a time slot. Many requests went unconnected. Therefore, the DC mode remained as the fall back operational mode until a better DAMA Channel Controller could be built.
Determining the time in which to transmit a message presented another significant problem because the distances between communications resources on a network result in propagation delays for the messages between the time they are transmitted until they are received. Thus, even if a time slot was found in which a message could be transmitted, by the time the message reached its intended target receiver, the current time slot at the resource may already be allocated for some other message so that the target receiver would be unable to detect the first message.
Therefore, a need exists for an automatic system and method for determining the time slot in which a message may be sent so that the message reaches its intended destination at a time when it may be received.